Many environmental, reproductive, and genetic factors have been associated with an increased risk of breast and ovarian cancers. A family history of breast cancer has been identified as a major risk factor for the development of the disease. A genetic predisposition likely accounts for 5 to 10 percent of breast cancer and ovarian cancer. Approximately 80 percent of inherited early onset breast cancer is attributed to the breast cancer genes, BRCA1 and BRCA2. Among families with the same BRCA1 (BRCA2) mutations, there are differences in age-specific penetrance, lifetime penetrance, proportions of breast and ovarian cancer, and risks of other cancers. This variability suggests there are environmental and genetic factors interacting with the BRCA1 and BRCA2 genes. The identification of predictors of phenotypic expression, not only in terms of type of cancer but also in modulating age at onset, has implications for screening and prevention strategies for women at significantly increased risk of breast and ovarian cancers due to the BRCA1 and BRCA2 genes. This is a proposal to examine the effects of reproductive and genetic factors which may modulate the incidence by age and overall incidence of breast and ovarian cancers in individuals with BRCA1 and BRCA2 mutations. The cohort is composed of Caucasian and African American BRCA1 and BRCA2 mutation carriers. We have already sampled 215 BRCA1 and 141 BRCA2 mutations carriers in our Utah kindreds and will continue to sample within these families to identify all mutation carriers. Little information is available regarding prevalence of BRCA1 and BRCA2 in African Americans, although for women less than 44 years of age, their incidence of breast cancer is higher than for Caucasians. With collaborators in Dallas and Chicago, we propose to contact African American families with a history of breast and/or ovarian cancer, to identify BRCA1 and BRCA2 mutations, and sample within those families to identify all mutations carriers. The cofactors to be examined in this cohort include ages at menarche and menopause, parity, age at first pregnancy, use of oral contraceptives, and hormone replacement therapy. The genetic factors to be investigated include the h-RAS VNTR and carcinogen metabolizing genes GSTT1, GSTM1, CYP2D6, CYP1A1, and EPHX. Survival analysis models will be used to estimate cumulative incidence by age and overall incidence for breast and ovarian cancers stratified by the hormone, reproductive, and genetic factors.